This invention relates to pistons for internal combustion engines.
The piston of this invention is of the type having flexible skirt portions and is an improvement on my earlier U.S. Pat. No. 2,802,707. As stated in my patent, some of the reasons for providing skirt sections which are flexible are to afford substantially uniform pressure and bearing engagement throughout the skirt bearing areas, to reduce skirt friction, to avoid scoring, to compensate for expansion and to avoid seizing. The piston disclosed in my patent had upper and lower struts which supported the skirt sections and which were reversely curved to an acute angle. These struts provided flexibility and at the same time provided a degree of stiffness to withstand side thrusts imposed by the motion of the connecting rod and to compensate to some extent for the rocking forces which develop during high speed engine operation. These rocking forces are concentrated at the top and bottom of the skirt sections.
One of the objects of the present invention is to deal more effectively with these rocking forces, that is to more effectively resist such forces while still retaining enough flexibility in the support of the skirt sections to reduce skirt friction, compensate for expansion and generally serve the purposes of flexibility referred to above. I have found that the rocking forces on the piston are concentrated with greater intensity at the bottom than at the top of the skirt sections and accordingly I now employ struts for the lower end portion of the skirt sections which are bent to a substantially larger angle than is shown in my patent. This substantially larger angle may be in the range of about 90.degree. to 180.degree. and sufficiently stiffens the lower end of the skirt sections to resist the rocking forces which develop during high speed operation. A substantially straight or 180.degree. angle would ordinarily be suitable only in an extra long skirt section and of course would allow very little flexibility at the lower end of the skirt sections.
The struts supporting the upper portion of the skirt sections in my improved construction retain substantially the same degree of curvature as shown in my patent. The greater flexibility provided by these upper struts is sufficient to make the skirt sections as a whole sufficiently flexible for the purposes intended and yet provide enough stiffness to withstand the lesser concentration of forces at the top of the skirt sections which develop due to rocking.